Thermal conduction heater wells have application for removing contaminants from soil, groundwater or rock. Thermal conduction heater wells are heating devices that are typically placed into the ground or soil pile to deliver heat energy into a contaminated media. In most applications, drill rigs are used to auger holes into the ground to install a metal casing that can accommodate a heating device to transfer heat to the contaminated surroundings. Existing designs of electrical heater wells have focused on the use of tubular electric heaters for heat generation inside metal casings. These heaters are stiff and difficult to install, especially if the heater is significantly long. Traditional heater designs provide uniform heating over the length of the heater with no ability to alter and adjust the heating at different intervals. Conventional systems are also bulky, typically requiring a casing diameter of six inches or greater to accommodate the heater inside the casing and special equipment to install the large casings and heater components.
Heaters comprised of stiff tubing are also currently used; stainless steel is a common material of construction. Cranes or lift equipment are required to elevate the stiff, pre-constructed, heaters to vertically place them into metal casings below grade. Long conventional heaters must be manufactured on-site because they are too long to ship when pre-constructed. There is no way to change the amount of heating energy delivered for different depth intervals of the heater during the project.
Another thermal conduction heating technology includes installing casings in the ground and pushing hot gas internally through the casing to heat the subsurface. The hot gas is usually supplied by a number of natural gas or propane burners and each burner requires an expensive control system and safety measures. This presents problems such as inefficient energy usage due to the large amount of heat loss in the hot gas exhausted to the air from the heaters and the build-up of acidic condensate in the piping systems during early phases of heating. These gas injection piping systems utilize a pipe inside a pipe and therefore are also bulky and heavy. The minimum outside pipe diameter for these systems is typically four to six inches in diameter. Like tubular electrical heaters, gas heater wells have no practical method to vary the heat output at various depths.
The current practice in subsurface heating continues to be the installation of stiff tubular heaters that are difficult to ship and install and that cannot be modified to provide heating at different depth intervals or easily modified during differing stages of the project. The systems are bulky and require borings of large diameter to support the heater elements.